Differential amplifiers are used in many applications. One such application is to translate voltage levels from one logic type to another. For example, differential amplifiers may be used to translate from an ECL voltage level to a CMOS or TTL voltage level. Currently, many integrated circuits are designed to make use of different technologies, such as ECL, TTL, CMOS and BiCMOS, throughout a circuit. Hence, it is important to be able to quickly and accurately translate levels between circuits having different technologies.
Most differential amplifiers include a pair of transistors driven by respective input signals. If the transistors are NPN transistors, for example, the collectors of the transistors will be connected to V.sub.CC via a load, the bases will be connected to the respective input signals and the emitters will be connected to a common current source. The higher input signal will drive the respective transistor to draw more current, and hence, will reduce the voltage at its collector, as more current is drawn through the respective load. Often, a resistor is used as a load; however, a resistor will not provide a full voltage swing between the voltage rails. On the other hand, active load may be used to provide a full voltage swing, but these loads may result in the forward-biasing of the differential NPN transistors, which will slow the circuit.
Therefore, a need has arisen in the industry to provide a high speed differential amplifier which may be used in level translation, among other applications.